Typical materials requiring surface flatness at high level include a single-crystal silicon disk called a silicon wafer for producing semiconductor integrated circuits (IC, LSI). The surface of the silicon wafer should be flattened highly accurately in a process of producing IC. LSI etc., in order to provide reliable semiconductor connections for various coatings used in manufacturing the circuits. In the step of polishing finish, a polishing pad is generally stuck on a rotatable supporting disk called a platen, while a workpiece such as a semiconductor wafer is stuck on a polishing head. By movement of the two, a relative speed is generated between the platen and the polishing head while polishing slurry having abrasive grains is continuously supplied to the polishing pad, to effect polishing processing.
As polishing characteristics of a polishing pad, it is requested that a polished object is excellent in planarity and within wafer non-uniformity and a polishing rate is large. A planarity and within wafer non-uniformity of a polished object can be improved to some extent with a polishing layer higher in elastic modulus. A polishing rate can be bettered by increasing a holding quantity of a slurry on a foam with cells therein.
A polishing pad comprising a non-foamed synthetic resin or a polishing pad comprising a polyurethane foam has been proposed as a polishing pad satisfying the above properties (Patent Documents 1 and 2).
However, when a polishing pad comprising a foam is used, there is a problem such that scratches (flaws) are likely to occur on the surface to be polished of an object to be polished because the contact area between the object to be polished and the polishing pad becomes smaller and local surface pressure becomes higher.
On the other hand, when planarization process of a large number of semiconductor wafers is performed using a polishing pad, a fine uneven portion of the surface of the polishing pad is worn to deteriorate the performance of supplying a slurry to the processed surface of the semiconductor wafer, to decrease the polishing speed, or to worsen the planarization characteristics. Therefore, after having performed the planarization process of a predetermined number of semiconductor wafers, it is necessary to renew/roughen (dressing) the surface of the polishing pad using a dresser. When dressing is carried out for a predetermined period of time, uncountable fine uneven portions are produced on the surface of the polishing pad, so that the surface of the polishing pad becomes fluffy.
A conventional non-foamed polishing pad has a problem such that a cut rate is low at the time of dressing and such dressing takes too much time.